A wipe effect is carried out using a production switcher which receives first and second synchronized video signals (video 1 and video 2) by generating a control signal which is synchronized to the video signals and varies in a predetermined fashion between two exteme values, which may be represented as one and zero. For example, in the case of a horizontal wipe, in which the transition between two input scenes appears as a vertical line or stripe which moves across the output scene from one side to the other, the control signal has a ramp waveform which repeats at line rate, the start point of the ramp progressing through the line interval from field to field. In a preset pattern wipe, the control signal is designed so that a selected portion of the background scene (video 1) is replaced by the corresponding portion of an insert scene (video 2), and the size of the area of the output scene that is occupied by the insert scene increases to a preset limit while its geometrical shape remains the same.
The output signal video C of a video mixer which receives the video signals video A and video B and a control signal may be expressed as EQU video C=control X video A+(1-control) X video B
If video B represents black (which may be achieved by grounding the video B input terminal of the mixer) and the value of the control signal is increased from zero to one, the video C scene is a progressively darker replica of the video A scene. Mixing of a video signal to ground in this manner can be used to provide a shadow effect.